In many applications and especially in the measuring of a skin fold, it is necessary that the caliper arms be urged together by a constant force. For instance in the measuring of a skin fold, the skin is pulled out or pinched and the caliper is used to measure the thickness of the double layer of skin for an indication of the physical condition of the individual. Naturally the skin in being pliable can render different measurements if different pressures are applied to the caliper arms. One past attempt to supply constant pressure calipers is exemplified in the U.S. Pat. No. 3,008,239, issued on Nov. 14, 1961, with Karl O. Lang as inventor. In this patent a pair of caliper arms are mounted on meshing gear wheels with one gear wheel having a tension spring pivotally connected thereto to return it to the closed arm position. An understanding of basic geometry illustrates that there can be a variance in the force exerted on the caliper arms because of the change in the lever arm length through which the spring acts. However the instrument is constructed to minimize this variance for the arm separation for which the caliper is normally used.
The overall purpose of the present invention is to provide a skin fold caliper in which the closing force on the caliper arms remains constant throughout a wide range of separation of the arms.